The present invention pertains to electronic phase shifting circuits and more particularly to Broadband Phase Shifting Circuits. The present invention accomplishes a phase shift by a phase inversion technique which permits a phase shift from 0 to 360 degrees without adding undesirable harmonics.
The application of a phase shifting circuit is necessary whenever a synchronous receiver is used, such as those used in oil exploration techniques such as the receiver portion of a magnetic resonance transmitter/receiver system. The frequency conversion circuits generally have three deficiencies.
Phase shifters, in general, are narrow band. That is, a phase shifter operates reliably only over a limited frequency range. The frequency range is normally limited to a 10 percent bandwidth.
Second, prior art variable length transmission line phase shifting circuits are also generally limited in the phase shift which they can provide at lower frequencies with managable equipment. Variable length transmission line phase shifting circuits rely on the difference in path length to accomplish a phase shift between signals. Thus to achieve a significant phase shift, at a low frequency, the difference in path lengths must be extremely large.
Third, phase shifting circuits operate on a frequency conversion principal which provides additional harmonic frequencies of the frequency desired. This means that higher harmonics of the desired frequency will be produced to such an extent that the higher harmonics will provide inaccuracies in the measured signals. This requires the addition of electrical filters, adding costs over and above the costs of the phase shifting circuit itself.
Thus, phase shifting circuits available today are very limited not only in the bandwidth in which they will operate but also in the phase shift which the circuit will provide. In addition to the bandwidth limitations, phase shifting circuits also add inaccuracy to measurements by the nature of the principal on which they operate.